Well my other thought is that when doing it that way you add 1 more connection which is an additional point of loss / corosion. Is the loss from that connection made up in any way by the (potential) lower resistance value of the dual 30 Amp lines?
Would splitting the lines decrease the heat generation or increase disapation versus the 1 50 amp line?

Since the 30 amp lines are priced lower than the 50s' by more than an order of magnitude, are they made of much lesser quality? Can this affect the expected savings in resistance?

My personal guess is a splitter at the post and 2 cords would be best as 30 amp cords are much cheaper than a single 50 amp cord. Also easier to handle.

Usually the second is for the air conditioning especially if you have two AC units.

30 amp cords are cheaper as the wire does not need to be as thick. As they get thick they can wear quicker too so they need to make them even thicker yet. 50 AC amps is serious power (30 isn't a joke). Something goes wrong and it's bad.

The splitters are not cheap. The Marinco ones are most common. This way you can plug into two pedestals with 30 amp cords as well as one 50 amp. That is more flexible than one 50 amps cord and a splitter on the other end. You can use tie wraps to join the two cables.

Antares: Doghouse already has all the cables and adapters known to man, so relative cost isn’t an issue. The quality is generally consistent between the same manufacturer's different sizes.

Sully: Indecision is the ultimate key to flexibility.

OK Gordy, please dazzel me...
Can I trade this job for what's behind door #1? I thought I wanted a career, turns out I just wanted paychecks.

Do you:
A. I would: Use 1 50 Amp cord and split it at the boat.
B. I would not: Split the 50 Amp and run 2 30 Amp cords.

C. Other - Explain
Simplicity. Why run 2 cords, when 1 will do?
People tend to make things way too complicated. The world has all these supposedly complex problems, but I'm telling you, simple solutions are all that are needed.
For instance...
Complex Problem: High gas prices.
Simple Solution: Lower the prices.
What? It's not like oil companies need a real reason to raise the prices, so why do we need to come up with any further motivation to lower them?

Please also explain why your situation is best.
My situation is best, because someone famous “said so”. Remember, people will accept your ideas much more readily if you tell them that Benjamin Franklin said it first.

My turn: Why is it that, in just two days, tomorrow will be yesterday? Explain, and illustrate.

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Gord May "If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

Gordy,
Holy Cow! That was fantastic I have not laughed that hard in weeks. Thank you, I needed that.

I am putting this theoritical discussion out there to determine the best course of action. Since I did not get an engineering disertation on the differences in AGW / AMP ratios (YET) I will guess that it is safe to say there difference is nominal.

Cost is always a factor, but you also have to weigh that vs the SWMBO happyness factor. Then again I can take her out to dinner at the marina rather than her cooking for the difference in price. (Many times over)

Thanks Gordy! As usual your sage advice is well recieved. However... ssulivan. Pblias and I feel the flexability of (2 ) 30 amp cords is an advantage albiet when purchasing the original solution. As was mentioned it is usually the Airco on the second 30 amp leg. Some cruisers only use this a few times last year. It really depends on the usage. Mirinco 30 amp last week $49.95

"A 50A 125V (only) cord, which is 6 gauge copper (.5 ohms per 1000 ft), has less than half the DC resistance as a 30A 125V cord, which is 10 gauge copper (1.25 ohms per 1000 ft) of the same length. So for a 50 ft 6 gauge cord carrying 50A, voltage drop is about 2.5V (or just over 2% at 120V), while a pair of 30A cords, each carrying 25A, would drop about 3.1V (or 2.6%).

Since the number of connections remains the same, the impedance of those is independent of how long each cord is.

Higher voltage drop will only cause more current flow in induction motors operating under constant load, which could be a problem if you have large AC motors on board. I'd be more concerned with the voltage supplied (under load) by the marina - the ones I've tested seem to have pretty flabby voltage (voltage is all over the place as loads are switched in and out)."

While this is almost completely correct, there is 1 additional connection which also introduces additional resistance in the Dual 30 Amp setup.
1 at pedistal 2 at y 2 at boat vs 1 at pedistal 1 at y and 2 at boat.

Part of this discussion was to determine the cost effectiveness of purchasing the necessary cords, but also to determine what the best configuration woudl be for use. The total voltage drop would be so minimal the additional expence in electricity would not provide a noticiable savings with a 50 amp cord.
The additional connection is another watch point for corrosion.

The least expensive way is to have the y and 2 30's.
The best is to have all 3. Incase a pedistal is far away and you can run the 50 to the Y to 2 30's, or just run the 50 to the splitter if you don't want to muck with multiple cables.

I would prefer to keep the greater length of cable rated to the upstream overcurrent protection.
A 50 Amp receptacle will be protected by a 50A breaker.
A 50A cord will be #6AWG Cu. Conductors; whereas a (pair of) 30A cord will be #10AWG & seriously undersized for the 50A supply.

Being relatively small, the reverse “Y” Adapter is more subject to theft than is the Cord, so will be more secure located aboard the boat (than on the dock).

We use two 30 amp cords directly into two 30 amp outlets if the pole has a separate circuit for each 30 amp outlet. That way, there's a full 30 amps to both cords which may be needed in the boat. Every little bit helps if you have a high demand for electric as we do dockside. We use the 50 amp splitter at the pole when it's more practical, ie: only one 30 amp outlet or a single circuit. A 50 amp cord is a bear to handle and store as well as the high cost everyone has already mentioned. And if you need to replace the plug ends, that's also very costly and hard to do.
We've replaced plug ends on 30 amp cords, which is easier to do, trimming back until you get clean wire. These cords come in handy at marinas where you don't need a 50 ft cord or if you need a shorter extension as was mentioned above..

The comment above about 'A single cable is easier to arrange neatly from pedestal to inlet.' is true but really has no bearing applied to this. You can easily link the cables together with wraps of some kind or even the sleeve they make for power cords.

This info comes from 10 years experience with this arrangement. We have the option of both on our boat, two 30 amp inlets and one 50 amp inlet. When we bought our boat, the wife thought she'd surprise me and bought a 50 amp cord. I immediately returned the 50 amp cord and bought the two 30's and splitter. Expense alone was worth it. But the 50 amp cord was just too much.
One final thing. If your pole only has two 30 amp outlets and they're on the same circuit you're not getting enough to supply 50 amp requirements in the boat.

... We use the 50 amp splitter at the pole when it's more practical, ie: only one 30 amp outlet or a single circuit. A 50 amp cord is a bear to handle and store as well as the high cost everyone has already mentioned...Scott

Should you ever suffer a fire, you may find that you're insurance won't cover your loss; based upon that very clear code & good practice violation.
Connected to a 50A receptacle, your 30A cord(s) is/are seriously undersized.
Of course, adapting a 50A cord to a 30A inlet, at the load end, is also a violation; but slightly less egregious.
Good luck, and I hope you get another 10 years of safe service from your inadequate arrangement.

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__________________
Gord May "If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"